The present invention is directed to a light directing arrangement and method for use with a display apparatus, and more particularly to a light directing arrangement that is resistant to corrosion and directs an image to an angle different from a glare angle.
Liquid crystal displays (LCD) are used in many different types of electronic devices, including portable computers, cellular phones, and digital watches. One class of LCD, which is substantially reflective, often includes a reflector for directing ambient light to the viewer. Another class of LCD often includes a partially transmissive reflector for also allowing light from a light source within the device to convey information to the viewer. A partially transmissive reflector is commonly called a transflector, and an LCD that incorporates a transflector is commonly called transflective. The reflector may be made of metal or other types of composite materials. Some examples of LCD devices are discussed in co-pending application, xe2x80x9cOptical Devices Using Reflecting Polarizing Materialsxe2x80x9d, Ser. No. 09/298,003, filed Apr. 22, 1999.
The present invention is a display apparatus that provides protection against corrosion for a metallic layer. The display apparatus includes a light modulating layer sandwiched between two polarizers and a light directing film. The light directing film includes a prismatic structure having two sides, where one side includes saw-tooth formations having tilted surfaces, and a metal layer on the side of the prismatic substrate having the saw-tooth formations. The tilt angle of the tilted surfaces offsets an optimal viewing angle for the display from a glare angle for the display.
In a first embodiment of the invention, the light directing film of the display apparatus further includes an inorganic protective layer formed on the metal layer, wherein the inorganic protective layer inhibits molecular transfer to the metal layer and balances the color of reflected and transmitted light. The light directing film further includes a pressure sensitive adhesive layer between a polarizer and the inorganic protective layer.
The pressure sensitive adhesive layer may be an acrylate acrylic acid adhesive layer, the adhesive layer being optically diffuse, wherein the adhesive layer inhibits corrosion of the metal layer, in one embodiment of the invention. The pressure sensitive adhesive layer may include optical diffuser particles. The inorganic protective layer may be one or more materials selected from the group consisting of titanium, indium tin oxide, zinc sulfide, tin oxide, indium oxide, titanium oxide, silicon dioxide, silicon monoxide, and magnesium fluoride. The metal layer may be selected from one or more of the group consisting of silver, chromium, nickel, aluminum, titanium, aluminum-titanium alloy, gold, zirconium, platinum, palladium, aluminum-chromium alloy and rhodium. The metal layer is preferably silver. The prismatic structure may be made of cured resin, such as a UV curable cross-linked epoxy-acrylate.
The display apparatus may also include a light cavity for providing light to the light modulating layer, adjacent to the prismatic polymer substrate, wherein the metal layer is partially transmissive.
The tilted surfaces of the prismatic layer may have a tilt angle of about 1xc2x0 to 35xc2x0 from horizontal, more preferably about 3xc2x0 to 12xc2x0 from horizontal, and most preferably about 6xc2x0 to 9xc2x0 from horizontal, in one application. The saw-tooth formations may have a repeat distance of about 5 microns or more and about 200 microns or less, more preferably about 30 microns or more and about 80 microns or less, and most preferably about 50 microns, for one application.
In a second embodiment of the present application, a polymer protective layer is formed over the metal layer to protect the metal layer from corrosion. The light directing film also includes a diffuse adhesive layer formed over the polymer layer, attached to the polarizer. The polymer protective layer protects the metal layer from the mobile reactive species in the adhesive layer. The polymer protective layer may be selected from a group consisting of cross-linked epoxy, cross-linked or linear acrylic resin, soluble polyester, polyethylene, polyvinylidene chloride, polyvinyl alcohol and polymethyl methacrylate.
The polymer protective layer may be formed by solution coating in a preferred embodiment, in which case the thickness can range from about 0.01 micron to about 50 microns. Alternatively, the polymer protective layer may be formed by the vapor deposition and subsequent curing of a polymer precursor onto the metal layer. The protective layer may be cured using a process selected from the group of thermal radiation, ultraviolet radiation, electron beam radiation, plasma exposure and corona exposure. In the case of formation using vapor deposition, the polymer protective layer may have a thickness of about 1 nanometer to 2 micrometers.
Alternatively, the polymer protective layer may be formed by a plasma process selected from the group consisting of plasma-polymerization and plasma-enhanced chemical vapor deposition. Preferably, the polymer protective layer is a solution coated polymethyl methacrylate. Preferably, the metal layer is a silver layer having a thickness of about 400 Angstroms. The diffuse adhesive layer may preferably be butyl acrylate acrylic acid adhesive.
The display apparatus of the present invention may include both the inorganic protective layer and the polymer protective layer.